The present invention relates to an apparatus for applying process solution, such as resist solution, to coat a substrate with a film of the process solution in a process of manufacturing, for example, a semiconductor device or a LCD.
In the step of performing photolithography to manufacture a semiconductor device, a wafer is coated with resist solution, thereby forming a resist film on the wafer. The resist film is exposed to a predetermined circuit pattern and then developed, thus forming a specific pattern in the resist film.
To coat wafers with resist solution, spin coating is generally utilized. In the spin coating, a wafer is held on a spin chuck by means of vacuum suction. The resist solution is dripped onto the wafer while a motor rotates the wafer. The solution spreads over the entire surface of the wafer by virtue of centrifugal force, forming a resist film having a predetermined thickness. A pump, such as a bellows pump, is used to drip the resist solution onto the wafer. That is, the pump discharges the solution in a prescribed amount and at a predetermined rate.
In recent years, device patterns have become more complex, each consisting of more components arranged in higher density. The thickness uniformity of resist film is therefore considered very important. Since resist solution is expensive, it is necessary to apply the solution to a wafer in an amount as small as is possible. Hence, it is demanded that the resist solution be applied in a small amount and that the resist solution forms a resist film having a uniform thickness.
To meet the demand, the conditions of applying resist solution to a wafer must be minutely controlled in accordance with the physical properties of the resist solution. These conditions cannot be controlled in the conventional apparatus and method for applying resist solution. Particularly in a conventional apparatus, wherein nozzles are interchangeably used, one at a time, to apply various types of resist solutions to wafers, the resist solutions are applied at the same rate though they differ in physical properties. Consequently, it is difficult to form resist film having an appropriate uniform thickness.